prevent large files from being cached in memory (backups!)

nocache <I/O-heavy-command>
We all know... nice -n19 for low CPU priority.   ionice -c3 for low I/O priority.   nocache can be useful in related scenarios, when we operate on very large files just a single time, e.g. a backup job. It advises the kernel that no caching is required for the involved files, so our current file cache is not erased, potentially decreasing performance on other, more typical file I/O, e.g. on a desktop.   http://askubuntu.com/questions/122857 https://github.com/Feh/nocache http://packages.debian.org/search?keywords=nocache http://packages.ubuntu.com/search?keywords=nocache   To undo caching of a single file in hindsight, you can do cachedel <OneSingleFile>   To check the cache status of a file, do cachestats <OneSingleFile>

These Might Interest You

  • "That's it. Not much to see here. The first command writes any cache data that hasn't been written to the disk out to the disk. The second command tells the kernel to drop what's cached. Not much to it. This invalidates the write cache as well as the read cache, which is why we have the sync command first. Supposedly, it is possible to have some cached write data never make it to disk, so use it with caution, and NEVER do it on a production server. You could ... but why take the risk? As long as you are running a post 2.6.16 kernel,..." Source: http://ubuntuforums.org/showpost.php?p=3621283&postcount=1


    -1
    sudo sync && sudo echo 3 | sudo tee /proc/sys/vm/drop_caches
    StephenJudge · 2012-03-17 08:27:58 2
  • When you run a memory intensive application (VirtualBox, large java application, etc) swap area is used as soon as memory becomes insufficient. After you close the program, the data in swap is not put back on memory and that decreases the responsiveness. Swapoff disables the swap area and forces system to put swap data be placed in memory. Since running without a swap area might be detrimental, swapon should be used to activate swap again. Both swapoff and swapon require root privileges.


    10
    swapoff -a ; swapon -a
    alperyilmaz · 2009-03-25 03:30:41 0
  • This script creates date based backups of the files. It copies the files to the same place the original ones are but with an additional extension that is the timestamp of the copy on the following format: YearMonthDay-HourMinuteSecond Show Sample Output


    4
    backup() { for i in "$@"; do cp -va $i $i.$(date +%Y%m%d-%H%M%S); done }
    polaco · 2009-11-10 20:59:45 2
  • If you have a directory with lot of backups (full backups I mean), when it gets to some size, you could want to empty some space. With this command you'll remove half of the files. The command assumes that your backup files starts with YYYYMMDD or that they go some alphabetical order. Show Sample Output


    -1
    find . | sort | awk 'NR%2==0' | xargs rm $1
    sucotronic · 2013-07-11 07:36:18 0

What Others Think

Damn, that's useful!
flatcap · 264 weeks and 6 days ago
+1
wejn · 264 weeks and 6 days ago
For those on Ubuntu Precise, I have a backport of nocache in my PPA: https://launchpad.net/~fmarier/+archive/ppa/+index?field.series_filter=precise&batch=75&memo=75&start=75
fmarier · 262 weeks and 4 days ago

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Any thoughts on this command? Does it work on your machine? Can you do the same thing with only 14 characters?

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